The invention concerns a method for the electronic measurement of the thickness of very thin, electrically conductive films on nonconductive base material and apparatus for performing these measurements.
Direct mechanical measuring methods are no longer practical for measuring film thicknesses of less than 1 micron. Optical interference methods sometimes require considerable adjustment work and can be unacceptably affected by disturbing factors, such as the base material which supports the electrically conducting film. Electromagnetic eddy-current methods for determining the surface resistance of a very thin metallic film on a supporting foil are highly sensitive to inexact adjustment under certain circumstances. Measurement involving contact with the film usually cannot be performed due to the danger of damage to the film.
According to Olszewski and Cormack, "Contactless Measurement of Conductivity of Metals and . . . ", IEEE Transactions on Instrumentation and Measurement, Vol. IM-25, No. 3, September 1976, pp. 186-190, a time-domain eddy-current method is known, which, however, can be used only for metallic film thicknesses of 0.1 to 50 .mu.m.
According to Sterkhov and Tokarev, Measuring the Thickness and Conductance of Thin Films in the Course of Their Deposition, Izmeritel 'naya Tekhnika, No. 4, pp. 45-47, April 1974, a single open waveguide, whose aperture is covered with a dielectric plate, which in the course of the vapor depositions process is coated with the metallic film that is to be measured, can be used to measure the reflection factor arising in this way. However, the method is very imprecise in this way, with measuring errors of up to 30%, because in the extreme near field of a (unilaterally) open waveguide very complicated field conditions prevail, which are simplified if either a distance of at least a few wavelengths from the aperture is maintained or the waveguide continues on the other side of the film.